Due to land in August 2012, NASA's Curiosity Rover is intended to answer the big question about Mars - is it a suitable environment for life? The biggest and most powerful machine ever sent to Mars, Curiosity is a mobile lab packed with diverse scientific equipment and the information it uncovers could change the way we think about the iconic red planet forever. But before Curiosity can begin its mission of discovery, it must first pass the biggest test of all - landing safely on the Martian surface. By 2010, 38 attempts had been made to reach the planet. Only 19 had succeeded. Horizon tells the story of this unique journey of scientific discovery.